The present invention relates to a process for the production of microbial protein (referred to hereinafter sometimes as S.C.P.) and lipid from vegetable carbohydrates by culture of a microbe in a culture medium containing such carbohydrates. More particularly, the present invention relates to a process for the production of microbial protein and lipid from vegetable carbohydrates, especially starch, characterized by the two-step operation comprising liquefaction of starch by the action of dextrinogenic enzymes for preparing a culture medium for a microbe and saccharification of the liquified culture medium by aseptically adding a saccharogenic amylase to the culture medium while cultivating the microbe therein.
In recent years, single cell proteins are produced artificially from vegetable carbohydrates or mineral hydrocarbons by culturing a micro-organism. The proteins thus obtained originate from the cells of the cultivated micro-organism and are generally distinguished from those purely extracted from vegetable sources, such as beans, by a chemical means. These artificially produced proteins are useful as substitute for meat and find a wide variety of applications in food industry as substitute for meat, additives to foods and animal feeds, etc.
Hitherto, many studies have been reported on the production of S.C.P. from vegetable carbohydrates by culturing a microbe in a culture medium prepared from such carbohydrates. Used in these studies as starting material for fermentation or production of S.C.P. and lipid are carbohydrates represented typically by monosaccharides and oligosaccharides as well as starch, the latter being commercially available in a great quantity. Thus, the use of starch as starting material is desirable from the economical point of view. However, if a microbe used for culture can utilize only monosaccharides or oligosaccharides, starch or the like high molecular material must be previously hydrolyzed (saccharified) by some appropriate means before it is used for culture medium.
Typical conventional methods adopted for solving this problem are the so-called amylo process utilized for the production of alcohols from starch, the koji process and the election method between koji and amylo processes. According to these methods, koji (for example aspergillus oryzae) is cultured for several ten hours under suitable conditions in a preliminary step, preceding to the main fermentation process, whereby koji produces amylase which will be utilized for saccharification in the subsequent process. In this case, control and operation for the cultivation are complicated and the operation itself needs a prolonged period of time. Consequently, these methods are unsuited for such process as in the production of S.C.P. wherein a large amount of starting materials must be treated by a simple method within a short period of time.
Recently, the Symba process attracts public attention as a process for the production of S.C.P. from a waste water of starch processing. This process is a mixed culture (symbiotic) method wherein saccharification of thermally sterilized starch is carried out with a special kind of microbe (Endomycopsis fibligar) capable of producing amylase which is cultured in a separate fermentation tank in a main fermantation tank where the main yeast, Candida utilis, is cultured. However, if the initial concentration of the starch is high in the Symba process, a gelatinization phenomenon is surely expected to occur in the course of the thermal sterilizing treatment of the starch. It is surmised therefore that a limitation is inevitably established for the concentration of starch to be chrged into the process. As two different kinds of said yeasts are cultured together in the main fermentation tank, the well balanced growth between the two yeasts is taken up as a difficult problem. In addition, maintenance of the culture and the product of a stable quality is not easy in this process.
Under such circumstances, there is a great demand for development of a new process for producing S.C.P. from starch wherein culture of microbe is carried out easily and efficiently without any trouble.